3
alpha_s and quark masses Inclusive observables H.Stenzel 3 Lineshape measurements at LEP Measurement of cross sections and asymmetries around the Z resonance by the LEP experiments ADLO and SLD interpretation in terms of pseudo- observables to minimize the correlation combination of individual measurements and their correlation inclusion of other relevant EW measurements (heavy flavour, m W,m t,...) global EW fits to constrain the free parameters of the SM... in particular constraints on the mass of the Higgs... but also determination of α s Results: Phys.Rep. 427 (2006) 257 PDG 2006 LEPEWG 2006

16
alpha_s and quark masses Inclusive observables H.Stenzel 16 EW fit result for the Higgs Mass Claim: Theory uncertainty for Higgs does not include QCD uncertainties these are absorbed into the value of α s Purpose for the rest of this talk: evaluate QCD uncertainties

20
alpha_s and quark masses Inclusive observables H.Stenzel 20 dependence of the PO uncertainty on α s Increase of the observables uncertainty by a factor of ~2 for 0.11 < α s <0.13

21
alpha_s and quark masses Inclusive observables H.Stenzel 21 Evaluation of uncertainty for α s as obtained from an EW observable Technique based on the uncertainty-band Method: 1.Evaluate the observable O for a given value of α s 2.calculate the PT uncertainties for O using x µ scale variation at given α s 3.the change of O under x µ can also be obtained by a variation of α s 4.the corresponding variation range for α s is assigned as systematic uncertainty Uncertainty band method: R.W.L. Jones et al., JHEP12 (2003) 007

22
alpha_s and quark masses Inclusive observables H.Stenzel 22 Uncertainty for α s from EW observables For α s =0.119 the uncertainty is 0.0010-0.0012 Strategy adopted by LEPEWG: calculate QCD uncertainty of the observables in the covariance matrix included in the fit. Result: Δα s =±0.0010